Alpha-substituted thiobutyrolactones potentiate GABA currents in voltage-clamped chick spinal cord neurons

The effect of the experimental anticonvulsant, alpha-ethyl,methyl thiobutyrolactone (alpha-EMTBL), on gamma-aminobutyric acid (GABA) currents was examined in cultured chick spinal cord neurons using gigaseal recording techniques. alpha-EMTBL potentiated GABA responses in a dose-dependent fashion with half-maximal effect at 7 microM. alpha-EMTBL also augmented the response to maximal doses of GABA. In competition experiments, alpha-EMTBL relieved the block of GABA currents produced by saturating concentrations of picrotoxinin whereas diazepam and phenobarbital did not. At a single channel level, alpha-EMTBL increased the probability of opening GABA channels without significantly altering the mean channel open time or the single channel conductance. These results indicate that alpha-EMTBL potentiates GABA responses and has properties which distinguish it from benzodiazepines or barbiturates.